JPH0522848B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a thermal type installed in an intake pipe, etc., which is used as means for detecting the operating state of an internal combustion engine, for example, when electronically controlling the engine. The present invention relates to an air flow rate measuring device.

[Background Art of the Invention] When controlling an internal combustion engine electronically, the operating state of the engine is constantly monitored, a signal corresponding to the operating state is detected, and based on this detection signal, for example, the amount of fuel injection is adjusted. The settings are controlled. Such operating state monitoring means include engine rotational speed detection means, engine temperature detection means, exhaust temperature detection means, etc., and intake air flow rate detection means is one that is directly related to the engine operating state. exists.

As an air flow rate detection means used as a means for monitoring the operating state of such an internal combustion engine, there is, for example, a thermal air flow rate measuring device, which is a temperature-sensitive device having temperature resistance characteristics that is controlled by heating. This temperature sensing element is installed and set inside the intake pipe.

However, when the temperature sensing element of such an air flow measuring device is used in an air fluid for a long time, dirt adheres to the temperature sensing element, and as a result, the thermal conductivity of the temperature sensing element decreases. It will be in a state of decline.
Therefore, when measuring the air flow rate in response to the temperature change state of this thermosensor, the adhesion of the dirt will cause an error in the measurement output, and the function as an air flow rate will deteriorate significantly. become.

As a means to improve these points, for example, as shown in Japanese Patent Application Laid-Open No. 54-76182, the temperature-sensitive element is temporarily heated to a high temperature of, for example, 800 to 1000 degrees Celsius, and the temperature-sensitive element is It has been considered to perform burn-off to incinerate foreign matter that adheres to the surface. However, during such burn-off control, if the amount of heat applied to the temperature sensing element exceeds the allowable limit, the temperature sensing element and its supporting members will burn out, significantly impairing the functionality of this measuring device. It becomes like this. In addition, in order to execute and control such burn-off, a signal line is required for the control. For example, when used in an automobile engine control system, this system and a measuring device are connected. During this period, it becomes necessary to provide a special signal line for the above-mentioned burn-off, which results in a condition that affects the mounting restrictions on the engine.

[Purpose of the Invention] The present invention has been made in view of the above points, and it is possible to perform burn-off control to effectively incinerate and remove foreign matter adhering to a temperature-sensitive element, and to prevent problems such as burnout of the temperature-sensitive element. The present invention is a thermal type that enables the burn-off control to be carried out safely and effectively without causing any burn-off control, and to enable the burn-off control command signal to be easily installed and set without using a special signal line. It is an object of the present invention to provide an air flow rate measuring device.

[Summary of the Invention] That is, the thermal air flow rate measuring device according to the present invention periodically sets and energizes a temperature sensing element having a temperature resistance characteristic set in a measurement air flow using a heating synchronization signal. A heating current whose reference voltage is set based on the start signal is supplied, a temperature rise of the temperature sensing element to a specific temperature state due to this heating current is detected, and the heating current is cut off when the temperature rise to this specific temperature is detected. Make it. Then, the heating current for the temperature sensing element is made into a pulsed current whose time width is set in accordance with the air flow rate. Also,
When performing burn-off control, the energization start signal is configured with a burn-off command signal with a time width larger than the heating current time width in the case of the measurement heating control, and the temperature sensing element is not affected while this command signal is present. Set the heating current to be supplied continuously. and,
Furthermore, means is provided for detecting a state in which the temperature of the temperature sensing element reaches an incineration temperature state higher than the temperature at the time of measuring the air flow rate, and in this temperature rise detection state, the voltage value of the heating current to the temperature sensing element becomes low. The reference voltage is controlled so as to be set.

[Embodiments of the Invention] Hereinafter, embodiments of the invention will be described with reference to the drawings. FIG. 1 shows the configuration of a control system for an engine 11 to which an air flow rate detection device is applied. In this control system, the amount of fuel injection is electronically controlled in accordance with the operating state of the engine 11. It is. That is, the intake air from the air filter 12 is taken in through the intake pipe 13,
Throttle valve 1 driven by accelerator pedal 14
The fuel is supplied to each cylinder of the engine 11 through five portions. Inside the intake pipe 13, there is a temperature sensing element 1 constituting a thermal air flow rate detection device 16.
7 is placed and set. This temperature sensing element 17 is
It is constructed of a heater made of, for example, platinum wire, which is heated under electrical current control and has a temperature characteristic in which the resistance value changes depending on the temperature.

The detection signal from this air flow rate detection device 16 is configured by a microcomputer and is supplied to an engine control unit 18 including an engine control processing device. Heating is controlled by commands from the control unit 18.
The engine control unit 18 also receives a detection signal from a rotational speed detection device 19 that detects the rotational state of the engine 11, a cooling water temperature detection signal for the engine 11, an air-fuel ratio detection signal, etc. although not particularly shown in the figure. is supplied as the operating state detection signal. Then, in response to these detection signals, the unit injector 20 calculates the fuel injection amount that is most suitable for the operating condition of the engine 11 at that time, and sets the fuel injection amount to correspond to each cylinder of the engine 11.
A, 20b, .

In this case, the signal that sets the fuel injection amount is a pulse-like signal that sets the duty, and the data corresponding to the time width of this pulse-like signal is once set for each cylinder. The injector is controlled to open within the set time period by memorizing and stabilizing the registers 21a, 21b, . . . .

Here, the rotational speed detection device 19 includes cams 191 and 19 that are rotationally driven coaxially with the engine 11.
2, further includes a rotary plate 193 with a large number of teeth, and these cams 191, 192 and the rotary plate 1
93 for each electromagnetic pick-up 194~
196 and set up these pick-up 194
A signal corresponding to a specific rotational angle of the engine 11 and a signal for counting and detecting the rotational angular position are extracted from 196 to 196.

Fuel taken out from a fuel tank 23 by a fuel pump 22 is distributed and supplied to injectors 20a, 20b, . . . provided for each cylinder of the engine 11 through a distributor 24. . Here, the distributor 24
The pressure of the fuel supplied to the injector is controlled to be constant by the pressure regulator 25, and the amount of fuel injected is accurately controlled by the valve opening time of the injector section calculated above. The settings are now controlled.

The engine control unit 18 also gives commands to the igniter 26, and distributes and supplies ignition signals to the ignition coils 28a, 28b, . . . provided in each cylinder through the distributor 27. The engine 11 is controlled to operate in accordance with the operating state detection signal and is adapted to the operating state.

FIG. 2 shows the temperature sensing element 17 of the air flow rate detection device 16 used in the engine control system as described above. The wire 172 is wound and set. At both ends of the bobbin 171, shafts 173 and 174 made of a good conductor are provided as support shafts, and the shafts 173 and 174 are supported by pins 175 and 176 made of a good conductor, respectively. A heating current is supplied to the resistance wire 172 via these pins 175 and 176. The resistance wire 172 portion of the temperature sensing element 17 configured in this manner is set to be exposed to the airflow passing inside the intake pipe 13.

FIG. 3 shows another example of the temperature sensing element 17, in which a resistance wire 172 serves as a heating element with temperature characteristics.
is formed by printed wiring or the like on a film 177 made of an insulator, and this film 177 is supported and set by a support substrate 178 made of an insulator. Wirings 179a and 179b connected to the resistance wire 172 are formed on the surface of the substrate 178, so that a heating current is supplied to the resistance wire 172.

FIG. 4 shows an air flow rate sensing device 16 that is effectively used for the engine control system as described above.
This shows one embodiment, in which a temperature sensing element 17 is fixedly set inside the intake pipe 13 as described above, and an auxiliary temperature sensing element 30 is further set inside this intake pipe 13. ing. The auxiliary temperature sensing element 30 is made of a resistance wire made of platinum or the like having temperature resistance characteristics, like the temperature sensing element 17 described above, and corresponds to the temperature of the air passing through the inside of the intake pipe 13. The resistance value is set using the air temperature sensor and used as an air temperature measuring means. The temperature sensing elements 17 and 30 and the fixed resistors 31 and 32 constitute a bridge circuit. The connection points A and B are connected to the input terminal portion of the comparator 33 to detect the temperature change state of the temperature sensing element 17. Specifically, the comparator 33 generates an output signal when the temperature of the temperature sensing element 17 rises to a temperature state specified with respect to the air temperature.

The output signal from the comparator 33 which monitors the temperature state of the temperature sensing element 17 in this manner resets and controls the flip-flop circuit 34. Here, this flip-flop circuit 34 is set-controlled in response to the rise of the energization start signal from the control terminal 35. This flip-flop circuit 34 is configured as a level trigger type, and when the set command is at a high level, The set state is maintained regardless of the reset input. The set output signal from the flip-flop circuit 34 is sent to the output terminal 3 via the buffer amplifier 36.
7 as a measurement output signal, and the output signal from the amplifier 36 is taken out from the transistor 38.
is supplied to the base electrode of the flip-flop circuit 34 so that the transistor 38 is controlled to be in the on state when the flip-flop circuit 34 is in the set state.

This transistor 38 controls the supply of power to the bridge circuit including the temperature sensing element 17, and when the transistor 38 is on, a heating current is set to be supplied to the temperature sensing element 17. That is, the energization start signal is supplied to the flip-flop circuit 34, and after the flip-flop circuit 34 is set, the temperature sensing element 17 is turned on.
A heating current is supplied to the temperature sensing element 17 until the temperature of the flip-flop circuit 34 rises and the flip-flop circuit 34 is reset.

Here, the energization start signal is constituted by a rotation synchronization signal with a short pulse width that is generated in response to, for example, a specific rotation angle of the engine 11 while the air flow rate is being measured. Therefore, the flip-flop circuit 34 is set in response to the synchronization signal and reset in response to the rise in temperature of the temperature sensing element 17, and the time width of the heating current to the temperature sensing element 17 is set in response to the temperature sensing element 17. This state corresponds to the temperature change of the element 17, that is, the heat dissipation effect due to the air flow acting on the temperature sensing element 17, and the width of this heating current corresponds to the air flow rate in the intake pipe 13.

An output signal from a differential amplifier 40, which is supplied with the voltage value of the heating current supplied to the bridge circuit and a reference voltage from the reference power supply 39, is applied to the base of the transistor 38 as a control voltage. Supplied. The circuit including the differential amplifier 40 constitutes a constant voltage setting circuit that sets a reference voltage, and sets the heating voltage supplied to the bridge circuit including the temperature sensing element 17 as a reference.

In addition, it is made parallel to the series circuit of the temperature sensing element 17 and the resistor 31 of the bridge circuit,
A series circuit of fixed resistors 41 and 42 is connected, and a voltage signal at point C, which is the connection point between the resistors 41 and 42, is supplied to a differential amplifier 43. This differential amplifier 43 is also supplied with a voltage signal at point A, which is the connection point between the temperature sensing element 17 and the resistor 31, and the voltage signal at point A is the same as the potential at point C. It operates differentially so that a positive output signal is generated when the potential is higher than the potential of The output signal from the differential amplifier 43 is coupled to the base electrode of the transistor 38 constituting the constant voltage setting circuit in a state where it is superimposed on the output signal from the differential amplifier 40. Here, the values of the resistors 41 and 42 are the above C
The potential at the point is set to be equal to the potential at point A when the temperature of the temperature sensing element 17 reaches the incineration temperature of the attached foreign matter. The differential amplifiers 40 and 43 are configured, for example, as an open collector type, and the lower output voltage is applied to the transistor 38.

That is, in the measuring device configured as described above, in the normal measuring operation state, the energization start signal coupled to the control terminal 35 is synchronized with the rotation of the engine 11, for example, as shown in A in FIG. The flip-flop circuit 34 is set and controlled by this signal. Then, in response to the setting of the flip-flop circuit 34, the transistor 38 is turned on, and a heating current is supplied to the bridge circuit including the temperature sensing element 17, so that the temperature of the temperature sensing element 17 is increased as shown in FIG. It begins to rise as shown in B. In this case, the temperature rise rate of the temperature sensing element 17 corresponds to the air flow rate in the intake pipe 13, and when the air flow rate is large, the temperature rise rate of the temperature sensing element 17 is caused by the heat dissipation effect of the air flow. is delayed. Moreover, if the air flow rate is large, the cooling rate will also be fast, and the temperature at which heating starts will be low. Therefore, the time from the start to the end of heating is long.

In response to such a rise in temperature of the temperature sensing element 17, the resistance value of the temperature sensing element 17 changes to increase, and as the temperature of the temperature sensing element 17 rises, the potential at point A becomes lower than that at point B. When the potential at point A is lower than the potential, that is, when the potential at point A reaches the reference potential at point C as shown in diagram B, the output of the comparator 33 rises, and the flip-flop circuit 34 is reset. Therefore, in response to the setting and resetting of the flip-flop circuit 34, the transistor 38 is controlled on and off, and the heating current to the temperature sensing element is controlled intermittently into a pulse state whose time width is controlled. Further, the output signal from the output terminal 37 becomes a rectangular pulse-like signal in a state corresponding to the heating current, as shown in FIG. 5C, and the pulse width thereof corresponds to the measured air flow rate. This output signal, for example, can be used as digital data by counting the pulse width using a clock signal, and is particularly useful for control units such as computers, etc. It can be used as is without any D conversion.

Here, the potential at point A is C as shown by the broken line D in FIG.
The potential at a point is shown by a solid line,
The output signal of the differential amplifier 43 is as shown by the broken line E in the figure. In this case, the output signal of the differential amplifier 40 is in the state shown by the solid line in FIG. The voltage of the heating current is set as a standard.

When foreign matter becomes attached to the temperature sensing element 17, burn-off control is executed as described above, and this burn-off control is executed by monitoring, for example, in the engine control unit 18. For example, it is executed when the engine 11 is stopped. When performing this burn-off, the energization start signal is composed of a burn-off command signal, and this command signal is composed of a signal with a large time width to set a sufficient incineration time as shown in Figure 6A. be done.

When the burn-off command signal rises, the flip-flop circuit 34 is set in response to the rise, similar to the measurement operation described above, and the heating current to the temperature sensing element 17 rises. Then, the temperature of the temperature sensing element 17 rises as shown in B in the same figure, and the temperature rises as the heating time passes and exceeds the temperature at the time of the above measurement, reaching the incineration temperature of the deposits. rises to. In this case, as the temperature of the thermosensing element 17 rises, the potential at point A becomes lower and an output signal is generated from the comparator 33. However, the flip-flop circuit 34 is configured as a level trigger type and is not energized. Since the heating signal continues, the flip-flop circuit 34 is held in the set state, and the heating current is continuously supplied, so that the output signal from the output terminal 37 becomes as shown in Figure C.

When the temperature of the temperature sensing element 17 reaches the incineration temperature state, the potential at point A and the potential at point C match, and the output of the differential amplifier 43 becomes as shown in FIG. 6D. , differential amplifier 40
The output signal of the differential amplifier 43 controls the transistor 38 to control the heating current and voltage so that the temperature of the temperature sensing element 17 is maintained at the incineration temperature state. This is what happens. FIG. 6E shows the state of the control signal to the base of transistor 38.

That is, when performing this burn-off, a heating current is supplied to the temperature sensing element 17 for a sufficiently long time range compared to the air flow measurement operation, and the temperature of the temperature sensing element 17 is raised to the incineration temperature state. . In this case, the time width of the burn-off command signal is set to a time width suitable for incinerating the foreign matter adhering to the temperature sensing element 17, but for some reason, the time width may be extended more than necessary. In this case, or if the synchronization signal level remains at a high level during normal measurement, there is a risk that the temperature sensing element 17 and its supporting member will be burnt out. However, in the above device, after the temperature of the temperature sensing element 17 reaches the incineration temperature state, the heating current power supply to the temperature sensing element 17 is controlled, and the temperature of the temperature sensing element 17 is reduced to the incineration temperature state. The temperature sensing element 17 is reliably protected from burnout.

[Effects of the Invention] As described above, according to the present invention, it is possible to effectively incinerate the foreign matter adhering to the temperature sensing element, and it is possible to perform maintenance so that the air flow rate can be measured with stable accuracy. In particular, this incineration operation is carried out in a state that reliably protects the temperature sensing element even if the burn-off command signal is long. In addition, the burn-off command signal for incinerating this foreign material can be supplied from a common control terminal together with the synchronization signal for normal measurement operations. In some cases, it can be very effective.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram illustrating an engine control system related to the present invention, and FIGS. 2 and 3 are diagrams each showing a configuration example of a temperature sensing element constituting an air flow measuring device used in the above system, FIG. 4 is a configuration diagram illustrating an air flow rate measuring device according to an embodiment of the present invention, and FIGS. 5 and 6 are signal waveform diagrams illustrating control states during measurement operation and burn-off, respectively, of the above embodiment. It is. 11...Engine, 13...Intake pipe, 16...
Air flow rate measuring device, 17... Temperature sensing element, 18...
Engine control unit, 30...auxiliary temperature sensing element,
33... Comparator, 34... Flip-flop circuit, 38... Transistor, 40, 43...
Differential amplifier, 41, 42...resistance.

Claims (1)

[Claims] 1. A temperature sensing element that has temperature resistance characteristics that are heated and controlled by a heating current set for the air flow path, and a time width in which burn-off control can be executed for a periodic synchronization signal that corresponds to the flow rate measurement operation. means for supplying a heating current to which a reference voltage is set for the temperature sensing element in response to an energization start signal that includes a burn-off command signal; means for correspondingly setting the heating current time width; means for outputting a pulsed signal corresponding to the set heating current time width as a measurement output signal; means for supplying and setting a heating current to the temperature sensing element in a time width set by the burnoff command signal in a state of a burnoff command signal having a time width longer than the burnoff command signal; means for detecting a temperature rise to a temperature state suitable for incinerating all the deposits; 1. A thermal air flow measuring device characterized by comprising means for setting the air flow rate to a lower state than the above.